Enhanced Q Improvement in Rectangular Shaped Inductors with Tapered Spirals

Rectangular outline shaped spiral inductors are most optimal from an RF circuit layout view point. However, they suffer from accentuated proximity effect losses due to current crowding effects. In this paper, quality factor (Q) improvement using layout optimized variable width and spaced (tapered) spirals is shown to be higher for rectangular inductors when compared to square inductors. It is also shown that Q improvement with tapered spirals increases with increased spiral thickness. Prototype rectangular tapered inductors are fabricated and measured using a 0.13 μ m BiCMOS process with different substrate resistivities.